1. Field of the Invention
This invention concerns disconnectable turret mooring systems for Floating Production, Storage and Offloading (FPSO) vessels and the like.
2. Description of the Prior Art
The prior art includes disconnectable mooring systems such as that described in U.S. Pat. No. 5,356,321 which is assigned to the assignee of this application. The mooring system includes a turret which is rotatably supported by a FPSO. A buoyant mooring member, called a xe2x80x9cspider buoy,xe2x80x9d is structurally connected to the bottom of the turret. Rotatable support is provided by an axial/radial bearing between the top of the turret and a moonpool sleeve in the vessel and a radial bearing at the bottom of the turret and the moonpool sleeve. The spider buoy carries risers from the sea floor to connect with pipes which run through the interior of the turret. Anchor legs or chains are connected between the spider buoy and the sea floor.
A selectively operable structural connector secured to the bottom of the turret connects to a hub extending upwardly from the top of the buoy. The above-mentioned U.S. patent illustrates a collet connector manufactured by Cooper Cameron of Houston, Tex. which acts cooperatively with a preload tensioning arrangement to provide a structural connection between the buoy and the turret. TORUS structural connectors manufactured by FMC Technologies of Houston, Texas have also been used in the past in the arrangement. The term TORUS is a trademark for such connector of FMC.
Other arrangements are known for selectively connecting a buoyant mooring member to a turret of an offshore storage vessel. U.S. Pat. No. 4,604,961 shows a turret which is rotatably supported on a vessel by bearings with the turret having a frusto-conically-shaped opening and with the buoyant mooring element having a frusto-conically-shaped skirt which fits cooperatively within the opening. A latching mechanism locks the turret to the buoyant member when the buoyant member is pulled fully into the opening.
U.S. Pat. No. 4,892,495 also shows a buoyant mooring member of a conical shape which is pulled into an opening of a turret which has a conical shape and is latched thereto when it is fully pulled therein.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a less costly coupling arrangement between the spider buoy and the turret of a disconnectable mooring system than previously known.
Another object of the invention is to provide a spider buoy/turret coupling arrangement with a resilient member which can resiliently absorb forces on a connection member while the buoyant member is being pulled into connection with the turret.
Another object of the invention is to provide a spider buoy/turret coupling arrangement which includes a sealing mechanism between the spider buoy and the turret so that seawater is prevented from entering the interior of the turret after the spider buoy is pulled into connection with the turret.
Another object of the invention is to provide contact rings between the bottom of the turret and the top of the spider buoy which are strong enough to support vertical and radial loads between the turret and spider buoy when the spider buoy is connected to the turret and can be machined with precision to provide close tolerances at a machining location away from the turret and/or the buoyant member such that the contact rings can be actually fit together before they are individually installed at the bottom of the turret and the top of the spider buoy.
The objects described above as well as other advantages and features of the invention are provided in a mooring arrangement having a turret rotatably supported on the vessel with a receiver structure at the bottom of the turret which has a female frusto-conically-shaped opening. A buoyant mooring member or buoy includes a male frusto-conically-shaped structure secured to its top end. The male structure or probe includes a hub secured at its top which is part of a hydraulic structural connector pair. The hydraulic connector is mounted at the top of the receiver structure and above the female opening at the bottom of the turret. When the male structure is fully pulled into the female opening, the hub is in registration with the hydraulic connector and can be latched thereto.
According to one feature of the invention, the male structure includes an interior resilient member which absorbs shock forces caused by pulling the male member into the female opening of the turret. Such structure, called a shock absorber cone, includes a stack of donut shaped resilient members within the male structure.
According to another feature of the invention, a sealing arrangement is provided between the male frusto-conically-shaped structure and the receiver structure at the bottom of the turret. A primary seal is established by an elastomeric ring on the outer frusto-conical structure of the buoyant element which engages an annular surface on the female frusto-conically-shaped structure of the receiver. Secondary sealing is provided by ports through a reaction ring of the receiver structure which lead to an interface between the exterior surface of the male probe and the interior surface of the female turret receiver. Sealing material can be forced through such ports if the primary seal were to leak.
According to another feature of the invention, the base of the conically shaped probe includes a ring of strengthened hardened steel with upwardly and outwardly facing surfaces provided thereon. A complimentary ring of strengthened hardened steel is disposed on the turret at the bottom end of the receiver and has downwardly and inwardly facing surfaces. The complimentary surfaces are machined in the hardened steel prior to fastening to the top of the buoyant member and the bottom of the receiver respectively and test assembled together prior to fastening to the buoy and to the turret. Fastening is by means other than welding such as bolts so as not to damage the hardened material of the rings by the heat of welding.